The present invention relates to a guide apparatus for guiding a movable contact glass supporting an original document places thereon for use in an electrophotographic copying machine.
Referring to FIGS. 1(a), 1(b), and 1(c), a conventional guide apparatus for guiding a movable contact glass, which serves as a support for an original and constitutes part of an exposure apparatus in an electrophotographic copying machine, will now be explained. In the guide apparatus, the contact glass is guided along straight rail members in the exposure scanning direction, so that the image of the original document is scanned and subjected to a slit exposure. The scanning light reflected from the original document is projected successively onto a photoconductor through an image formation member so that an image corresponding to the image of the original document is formed on the photoconductor. More specifically, in a conventional guide apparatus for such a movable contact glass as is cited in Japanese Patent Publication No. Sho 49-12184, the movable contact glass is guided by a pair of parallel rail members. One rail member is disposed along an upper edge of the contact glass and the other rail member is disposed along a lower edge of the contact glass. When a print button is depressed, the movable contact glass is automatically reciprocated, while being held between the rail members, so that the image of the original document can be scanned.
Referring to FIG. 1(a), there is shown a straight rail member A for guiding a movable contact glass B in the conventional guide apparatus. Above the rail member A there is located the center of gravity G of the movable contact glass B. In this guide apparatus, the image of the original document, is transported successively past an exposure position F. The actual distance L.sub.1 between the surface of a photoconductor drum C and an original document stacking surface D of the contact glass B should be maintained equal to an optical path L or a conjugate optical path which is determined by an image formation member, for example, an image formation lens E.
However, if the electrophotographic copying machine provided with the above-mentioned guide apparatus is made compact in size, the center of gravity B of the contact glass maybe moved beyond an upper position of the rail member A when the scanning is initiated or terminated as illustrated in FIGS. 1(b) and 1(c), so that a portion of the contact glass B on the side of the exposure position F tends to be moved upwards. When the original document stacking surface D is moved beyond the set optical path L, the image of the original document is not formed accurately on the surface of the photoconductor drum C. If the upward movement of the contact glass B is within the range that can be covered by the depth of focus of the lens E, it does not have an adverse effect on the image formed on the surface of the photoconductor drum C. However, if the upward movement is out of that range, it has an adverse effect on the image formed on the photoconductor drum C. This is a problem when ordinary lenses are employed. In particular, when light condensing optical elements whose depth of focus is small are employed, it becomes a serious problem.
Furthermore, when the electrophotographic copying machine is constructed in such a manner that one side edge portion of the contact glass is simply mounted on the rail member A in order to make the electrophotographic copying machine simpler in construction and less expensive, a gap greater than the permissible clearance between the contact glass B and the rail member A may be formed during reciprocation of the contact glass. From this point of view, it is required that the above-mentioned adverse effect be eliminated.
As a reciprocating drive apparatus for reciprocating the contact glass through the above-mentioned guide apparatus, a reciprocating drive apparatus as shown in FIG. 2 is known. This reciprocating drive apparatus can be used for reciprocating not only the contact glass but also other exposure optical systems.
In FIG. 2, a pin 4 is attached to a chain 3 trained over two sprockets 1 and 2. The pin 4 is fitted in a slot 5a of a bracket 5. A movable member 6, such as a contact glass or an exposure optical system, is mounted on the bracket 5. When the drive sprocket 1 rotates in the direction of the arrow, the chain 3 is rotated in the direction of the arrow. At this moment, by the movement of the pin 4, the bracket 5 and the movable member 6 are moved forwards from a start position St in the direction of the arrow and reach an end position E after having completed one stroke l. At this moment, the pin 4 is located at a left end position which is indicated by the imaginary line. With a further rotation of the chain 3, the movable member 6 is moved backwards from the end position E and is then returned to the start position St. Thus, the movable member 6 makes one reciprocating movement by one rotation of the chain 3.
In the drive mechanism for reciprocating the contact glass, which comprises the above-mentioned chain loop mechanism, two clutches are not required; rather, only one clutch is sufficient for moving the contact glass in the opposite directions.
Furthermore, starting, changing movement direction, and stopping the contact glass can be performed smoothly. By setting the stop position of the drive mechanism at the dead point of the pin 4 attached to the chain 3, the contact glass can be self-locked at its start position, without requiring any particular means. By this self-locking, the contact glass can be fixed automatically even if an outer force is applied thereto.
On the other hand, when the electrophotographic copying machine is not operated, there may be a necessity for moving the contact glass or its optical system manually to some desired position, for instance, for the maintenance of the copying machine or for moving jammed sheets from the copying machine. However, in the conventional electrophotographic copying machines, since the pin 4 (FIG. 2) is located at the dead point, the contact glass cannot be moved manually even if moving the contact glass by force is attempted. This is one of the shortcomings of the conventional electrophotographic copying machines having such a drive apparatus.
Usually, in the electrophotographic copying machines, the image of the original document is subjected to exposure scanning by reciprocating the contact glass or the exposure optical system, so that a latent electrostatic image corresponding to the image of the original document is formed on a latent electrostatic image bearing member. Furthermore, a sequence control of various copying steps is conducted in some electrophotographic copying machines. In order to conduct the sequence control, in the conventional electrophotographic copying machines, a pin 7 is secured to a lower portion of the bracket 5 as shown in FIG. 2. When the bracket 5 is moved forwards, the pin 7 kicks a control member 8, so that the control member 8 is turned counterclockwise about a shaft 9. At this moment, a stop pawl 8a of the control member 8 releases a one-way rotation clutch 11, such as a spring clutch, so that a pair of sheet feeding rollers 12 are rotated, whereby a copying sheet S which has been in a waiting position is transported in the direction of the arrow and reaches an image transfer section of the electrophotographic copying machine.
Thus, by utilizing the movement of the bracket 5, the control member 8 is operated and a controlled system, such as the sheet feeding mechanism, is operated with the proper timing. In the above-mentioned sheet feeding mechanism, the path of the pin 7 of the bracket is linear, and the control member 8 has to be operated one time during one reciprocation of the bracket 5. Therefore, it is required that, when the bracket 5 is in backward movement, the control member 8 be rectracted from the path of the pin 7 in order that the control member 8 not be operated. If the control member 8 is not designed so as to be retracted from the path of the pin 7 during the backward movement of the pin 7, the pin 7 may collide with the control member 8 and make it impossible for the bracket 5 to move backwards. Therefore, some means for retracting a top end 8b of the control member 8 from the path of the pin 7 is required. Various types of such means have been proposed, but they have shortcomings in that they are complicated in mechanism and erroneous operations are apt to occur.